Microbiological, Histological, Immunological, and Toxin Response to Antibiotic Treatment in the Mouse Model of Mycobacterium ulcerans Disease

Fred Stephen Sarfo,Jihui Zhang,Deepak V Almeida,Mark Wansbrough-Jones,Paul J Converse,Clive Robinson,Jacques H Grosset,Pamela L C Small

doi:10.1371/journal.pntd.0002101

Abstract

Mycobacterium ulcerans infection causes a neglected tropical disease known as Buruli ulcer that is now found in poor rural areas of West Africa in numbers that sometimes exceed those reported for another significant mycobacterial disease, leprosy, caused by M. leprae. Unique among mycobacterial diseases, M. ulcerans produces a plasmid-encoded toxin called mycolactone (ML), which is the principal virulence factor and destroys fat cells in subcutaneous tissue. Disease is typically first manifested by the appearance of a nodule that eventually ulcerates and the lesions may continue to spread over limbs or occasionally the trunk. The current standard treatment is 8 weeks of daily rifampin and injections of streptomycin (RS). The treatment kills bacilli and wounds gradually heal. Whether RS treatment actually stops mycolactone production before killing bacilli has been suggested by histopathological analyses of patient lesions. Using a mouse footpad model of M. ulcerans infection where the time of infection and development of lesions can be followed in a controlled manner before and after antibiotic treatment, we have evaluated the progress of infection by assessing bacterial numbers, mycolactone production, the immune response, and lesion histopathology at regular intervals after infection and after antibiotic therapy. We found that RS treatment rapidly reduced gross lesions, bacterial numbers, and ML production as assessed by cytotoxicity assays and mass spectrometric analysis. Histopathological analysis revealed that RS treatment maintained the association of the bacilli with (or within) host cells where they were destroyed whereas lack of treatment resulted in extracellular infection, destruction of host cells, and ultimately lesion ulceration. We propose that RS treatment promotes healing in the host by blocking mycolactone production, which favors the survival of host cells, and by killing M. ulcerans bacilli.

Highlights

Mycobacterium ulcerans infection is the cause of the neglected tropical disease, Buruli ulcer, found in poor rural areas of West Africa as well as in beach resorts in Australia [1] principally, transmission has occurred in every continent except Europe
Using a mouse footpad model of M. ulcerans infection where the time of infection and lesion development can be followed in a controlled manner before and after antibiotic treatment, we found that RS treatment rapidly reduced footpad swelling, M. ulcerans numbers, and ML production
We propose that RS treatment promotes healing in the host by blocking mycolactone production, which favors the survival of host cells, and by killing M. ulcerans

Summary

Introduction

Mycobacterium ulcerans infection is the cause of the neglected tropical disease, Buruli ulcer, found in poor rural areas of West Africa as well as in beach resorts in Australia [1] principally, transmission has occurred in every continent except Europe. Infection begins after exposure in slow-moving fresh water to plants or biting insects or other unknown mechanisms and slowly leads to swelling, manifested as a nodule, plaque, or edema in humans, and in experimental animals [4,5,6,7,8]. How soon ML production begins after infection is unknown [9] as is how soon it stops due to antibiotic treatment, currently rifampin and streptomycin [1], studies of human lesions have suggested production may be affected soon after treatment [10]

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Conclusion